1. Field of the Invention
The present invention relates to an idle-stop restart control system mounted mainly on a vehicle, for controlling restart of an internal combustion engine (engine) after idle stop by using a sensorless synchronous motor-generator which operates as a generator after the restart of the engine and also operates as a starting motor when the engine is to be restarted after the idle stop. The sensorless synchronous motor-generator does not use a position sensor for detecting a position of a rotor.
2. Description of the Related Art
In recent years, in vehicles using the internal combustion engine as a power source, idle stop is increasingly introduced for the purposes of improving fuel efficiency and reducing an exhaust gas. For further introduction of the idle stop, various idle-stop systems have been proposed.
As a method of calculating the position of the rotor based on estimation to control energization of an armature winding without a sensor for detecting the position of the rotor in an on-vehicle three-phase motor, a technique of controlling a sensorless brushless motor for driving a compressor for air conditioner, which is used for an electric automobile controller, has been reported (for example, see JP 07-115791 A).
However, the related art has the following problem. In a so-called self-control operation as in the conventional example described above, an induced voltage generated on the armature side is detected. From the detected induced voltage, the number of revolutions and an angular position of the rotor are calculated based on estimation. Based on the thus calculated number of revolutions and angular position of the rotor, the energization of the armature is controlled at optimal timing.
With a small number of revolutions which does not allow the energization to be controlled by the self-control operation described above, a motor is started by prospective control. In the prospective control, a rotational magnetic flux is forcibly applied to the armature, expecting that the rotor follows the rotational magnetic flux. This method is called an external control operation.
The self-control operation and the external control operation are known. The motor which can be started by the external control operation is limitedly used only when a load torque at the time of start is relatively small. Therefore, a starting motor for an internal combustion engine, with an extremely large load torque, cannot be started by the external control operation.